Football is here – and so is a new study on CTE

The NFL season begins this week, but America’s favorite sport has been on our minds for other reasons recently. New research released in the journal BMJ https://doi.org/10.1136/bmj-2026-100418 reveals that 1 in 4 former NFL players in this sample had CTE, a neurodegenerative brain disease caused by repetitive head injuries. Past studies already showed that football players are at high risk for CTE, but this study – which assessed ex-NFL players who died from 2016 to 2021 – revealed that at least a quarter of those former players died with CTE, and the study’s lead author says the actual numbers are likely higher. What does that mean for players (and fans) of American football? Short Wave host Nate Rott https://www.npr.org/people/348779465/nathan-rott and NPR sports correspondent Becky Sullivan find out. If you liked this episode, check out ourepisode on the brain injuries caused by operating blast weapons https://lnk.to/QDNSNj. Interested in more sports science? Email us your question at [email protected] mailto:[email protected]. Support public media with NPR+ and enjoy perks for over 25 podcasts like this one. This show’s perks include sponsor-free listening. Learn more at plus.npr.org http://plus.npr.org/. See pcm.adswizz.com https://pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences. NPR Privacy Policy https://www.npr.org/about-npr/179878450/privacy-policy

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• 0:22Speaker 01

  Shortwavers, hey, Nate Rott here. I live pretty much across the street from a high school football stadium. So this time of year, most afternoons, I can hear the sounds of practice from my house.

• 0:34Speaker 01

  And honestly, I love it. I love football. I love playing it in high school. I love watching it with buddies, like millions of other Americans do each Sunday. But like many football fans, I have also felt conflicted between loving the game and being horrified by the injuries people can get playing it. And a new study that came out last week really sheds light on one of the scariest risks of the sport, a degenerative brain disease.

• 0:58Speaker 02

  Yeah, it's called chronic traumatic encephalopathy, or CTE for short, that's the name that most people know. And it's caused by repetitive hits to the head, injuries to the brain.

• 1:08Speaker 01

  NPR sports correspondent Becky Sullivan is a good friend, and she's been covering this research, which I gotta say, Becky has been like, very sobering.

• 1:16Speaker 02

  Yeah, I mean, we've come to learn a lot about this disease over the years, right? Like, what it looks like in the brain, who's at risk for getting it. But I think one question has really loomed large this whole time, which is just how common is it, especially among football players, this really high-risk population? And so this study gets us closer to answering that question, at least for this very specific subset of former NFL players who died during a recent six-year period. And the researchers found, pretty definitively, that at least a quarter of those former players died with CTE.

• 1:46Speaker 01

  A quarter, so like, 1 in 4?

• 1:48Speaker 02

  Yep, and the study's lead author, a doctor named Daniel Danishfar, who directs a brain function lab at Mass General Brigham, says that number is the low end.

• 1:56Speaker 03

  Counting only the cases of CTE that we diagnosed ourselves, we found the minimum rate of CTE between 2016 and 2021 was 25%. At the upper end, the maximum rate of CTE was 98%. And so the true rate of CTE at death is somewhere in the middle there.

• 2:18Speaker 01

  Somewhere in the middle, but even if it is just like, 25%, that still seems shockingly high.

• 2:23Speaker 02

  It is, yeah. It's a really significant and serious finding. And really, that number is likely to be higher because of those they took a look at. You know, there are 600-plus players who died in that timeframe, whose brains weren't examined. And so at least some of them probably had it.

• 2:38Speaker 01

  Okay, so today on the show, the link between a brain disease and America's most popular sport. You're listening to Short Wave, the science podcast from NPR.

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• 4:20Speaker 01

  All right, Becky, let's really zoom in on the condition that players are getting here. Like, what exactly is CTE?

• 4:27Speaker 02

  Yeah, so like I said before, it stands for chronic traumatic encephalopathy. Basically, it's a neurodegenerative disease. There's some similarities there to something like Alzheimer's disease in terms of the traces it leaves in the brain. And actually, it's not something that you can be diagnosed with when you're alive.

• 4:41Speaker 01

  Whoa, so like, meaning you can't check to see if somebody has this in a living brain? You have to wait till they're dead?

• 4:47Speaker 02

  Well, yeah, I mean, you can't diagnose it from symptoms or an MRI or anything. And so to definitively diagnose this, you have to cut open the brain, check for this specific kind of tau protein, how it's collected around the brain. And this sort of fact of being unable to diagnose it in a living person is really kind of the big confounding issue with basically all CTE research. One researcher I talked to described it to me as sort of, essentially, just the evidence that you've been hit in the head, hurt your brain, and your brain had to repair itself. So it's sort of like a very characteristic scar.

• 5:17Speaker 01

  Like a brain scar.

• 5:18Speaker 02

  Basically. And it's been proven to be associated with repeated hits to the head. So like, concussions, obviously, but even just like little low-grade hits that accumulate over time, which is why it's linked to contact sports, of course, like American football, ice hockey. It's also, you know, potentially of concern for some combat veterans who might be exposed to things like blasts from weapons and other traumatic brain injuries.

• 5:39Speaker 01

  Yeah, we've covered this in the past, Becky, about the effect that operating blast weapons could have on soldiers that fire them. We'll link to that in the show notes. But you said it also has a lot of overlap with some other diseases. Like, what are the symptoms that people have?

• 5:53Speaker 02

  Yeah, I mean, this is a tough question to answer, but basically, the symptoms that are commonly associated with CTE, especially with like, advanced stages of the disease, are things like memory loss, depression, dramatic mood swings, maybe even to the extent of like, a personality change. But again, this stuff is really unclear because you can't diagnose it in someone who's living. So it's sometimes not clear if it's CTE causing these things or something else.

• 6:17Speaker 01

  Yeah, huh, that's so tricky. And in some ways, maybe surprising to me because we've known about CTE for a while now, right?

• 6:24Speaker 02

  Yeah, you know, I mean, in one sense, for like, a century, I mean, this was a thing with boxers way back in the early days of the 1900s, like, the 1920s. Nate, I think you've heard the phrase punch drunk. It describes sort of like, the wobbly walk and the slurred words of a longtime boxer that's taken a lot of hits to the head. And that's, of course, what we now think of as sort of classic post-concussion symptoms, the kind of thing that, you know, if you get hit big on the football field and you stand up and you're all wobbly and you can't walk straight, you'll get pulled off for a concussion.

• 6:52Speaker 01

  Concussion protocol, yeah, you're out.

• 6:54Speaker 02

  Exactly. And back in the 1920s, a doctor sort of found those effects of those hits and brain autopsies that he did on boxers. But our modern understanding of this disease really began, I think, in 2005, when the first diagnosis of CTE in a former NFL player was published. That was Mike Webster. He was this longtime center for the Pittsburgh Steelers.

• 7:14Speaker 01

  Yeah, it's interesting, Becky, because I feel like it took a long time after that 2005 study for CTE really to kind of become mainstream. Like, I first heard about CTE, or maybe I first really thought about it after Junior Seau died by suicide in 2012. And Junior Seau, if you're not a football fan, star linebacker for the San Diego Chargers.

• 7:33Speaker 02

  Yeah, he was only 43 when he died. He'd only just retired a few years before, actually, I think, which is just what made it so sad and brought so much media attention to it, especially because the way he died, this was so striking and very sad and terrible, was that he shot himself in the chest, and he didn't leave an explicit suicide note or anything like that. But that method of death, of course, preserved his brain for study.

• 7:55Speaker 01

  Yeah, and his brain was later diagnosed with CTE. And then, you know, there was the movie Concussion, like, all of which really caused public awareness amongst football fans and players, I feel like.

• 8:05Speaker 02

  Yeah, definitely. And in fact, it actually caused a lot of former players to donate their brains to science. And so now we have this brain bank that's housed at Boston University that has the brains of more than 300 former NFL players who either donated their brains to science themselves or whose families did more than 90% have been diagnosed with CTE. And this brain bank actually is a key part of this study, too.

• 8:26Speaker 01

  Yeah, can I ask, Becky, I mean, does that not skew the results if the sample we're looking at, right, is made up of people who like, self-identified or whose family said, hey, I think my family member had CTE?

• 8:37Speaker 02

  Yeah, definitely. I mean, that's actually really the whole thing with CTE research. And I've written about so many CTE studies where I make that point in the story of like, look, there's sample bias because 93% of all these NFL player samples in this brain bank have CTE, but you can't draw too many conclusions from that, for exactly the reason you say. And so that, of course, was on the mind of the authors of this survey, this study that we're talking about. Here again is lead author, Dr. Daniel Danishfar.

• 9:02Speaker 03

  And so whenever we look at the percent or the rate of neurodegenerative disease in specific brain bank populations, we know that it's not presenting an accurate picture of what's really going on with the overall population or sample. And so what we tried to do here was get a better sense of what that would look like.

• 9:26Speaker 02

  And so in this study that he worked on, you know, they talked about former NFL players specifically. So they set out to figure out sort of what this baseline number could be.

• 9:35Speaker 01

  Yeah. So how did they figure out that baseline number in this study?

• 9:37Speaker 02

  Well, so they looked at brain samples they had from players who had died between 2016 and 2021, since that's when they had the highest proportion of donors. And then they cross referenced that with basically every player who had ever appeared in even one NFL game since 1949 and died in that same time range. And so to come up with this range of possibilities, they did the math. Basically, on the low end, all the people who had donated and had confirmed CTE, which was 25% of this number. On the high end, there were only 20 confirmed donors with no CTE. And so maybe everybody else could have had it. That gives you that 98% number. But like we said before, the reality is somewhere in between.

• 10:16Speaker 01

  Yeah. Okay. So I understand like, there's a wide spread there.

• 10:19Speaker 02

  Yep.

• 10:19Speaker 01

  Again, like 25% minimum, to me, just feels so alarming.

• 10:25Speaker 02

  Yeah.

• 10:26Speaker 01

  NFL season is about to kick off. 22 guys are going to be playing on the field. I'm going to be watching it. How many of these players that I'm watching are going to end up with CTE?

• 10:36Speaker 02

  I mean, I think that's a big question, fair question to ask. And unfortunately, this study doesn't answer it. You know, it really only took a look at the players who died in that time period. And, and that's important because a lot has changed since the public awareness, as we're talking about, of the risks of concussions and head impacts has become more common. The average age at death of the guys whose brains are part of this brain bank was 66 years old. And that was a really important caveat pointed out to me when I talked to Dr. Randall Chestnut of the University of Washington.

• 11:03Speaker 05

  First of all, it was captured during a time when there was delayed recognition by the NFL that concussion was a big deal. So this may not represent NFL in 2026.

• 11:16Speaker 01

  Oh, interesting.

• 11:17Speaker 02

  Randall's a neurosurgeon. He works with athletes who have brain and spine injuries. He was not involved in this study, by the way. But basically, his point is that most of these guys played their careers a long time ago. We're talking about the NFL in the 70s, 80s, 90s. And football just looked a lot different then, you know?

• 11:33Speaker 01

  Yeah.

• 11:33Speaker 02

  Big hits were celebrated.

• 11:35Speaker 01

  Yeah.

• 11:35Speaker 02

  Absolutely. There was no really serious concussion spotting. Full contact practices at all ages were a lot more common. Helmets weren't sophisticated the way they are now. You know, even the NFL kickoff now looks totally different because of the risk of injury. And so, look, the risk of CTE is absolutely still there for players who play today, I'm sure. But that number of a quarter or more, that's just really impossible to say with today's players.

• 11:59Speaker 01

  Phew. Okay. Good to know. Let's move on to another question that researchers were looking at in this study, which is the rates of dementia and CTE. Did they find a link there?

• 12:09Speaker 02

  Yeah, I'm glad you asked about this, because I actually think that maybe this is the more interesting part of the study, because, you know, this popular conception of CTE, right? The popular idea of what it is, is that it's kind of basically a really scary form of early onset dementia, right?

• 12:24Speaker 01

  Yeah. I mean, you mentioned memory loss, personality change, suicidal ideation. I mean, those are all things we typically associate with dementia and CTE.

• 12:32Speaker 02

  Yeah, absolutely. And I definitely want to underline that that level of severe symptoms is rare, like even in the brain bank. Of those who had confirmed CTE, only a third had that highest stage, stage four, that's associated with those really dramatic symptoms. Basically, researchers were taking a look at this brain bank sample to try to figure out whether every individual had dementia or not. Some of them were diagnosed in life, so that was easy. But for others, they had to kind of like, look through medical records and compare that with interviews and records of family members.

• 12:59Speaker 01

  And what did they find?

• 13:01Speaker 02

  While they did find a very strong association with dementia in the highest stage of CTE, stage four, 90% of those guys had dementia. What I thought was really interesting is that there's actually really not much of a pattern with the other groups, because there's three other stages of CTE, 1, 2, 3. And then there's also those who didn't have CTE. And, you know, just for example, Nate, like 40% of the guys who were confirmed to not have CTE, did have dementia. Of the guys with stage three CTE, the second highest level, a little more than half of them had dementia. So like, the relationship actually isn't very clear.

• 13:33Speaker 01

  That really speaks to how complicated this whole thing is, man.

• 13:36Speaker 02

  Yeah, I think it just underlines dramatically kind of how little we know about the link between CTE, which is diagnosed after death, of course, and then the symptoms that somebody might experience in life. And there's just so much we don't know, and researchers are still working to figure out.

• 13:49Speaker 01

  Okay. So what do we do with this study then, Becky? Like, me, as a football fan, football season approaching, what should I take away from this?

• 13:57Speaker 02

  I mean, I think the prevalence finding that 25% at minimum number, that's really significant, it's really important. But to think of all the football players, you know, who are still alive, still playing, former players, it's important to talk about how, yes, CTE can't be cured, right? But all these symptoms that we've been talking about, that people popularly associate with CTE, they actually can be treated, right? Like, so players who are worried about it should seek treatment for these things.

• 14:22Speaker 06

  So our concern is that the public and kitchen table conversations around CTE are creating hopelessness in living former NFL players. And this hopelessness may discourage them from reaching out to their doctors and getting treated for conditions like sleep apnea that are causing worrisome symptoms.

• 14:39Speaker 02

  Rachel Grashaw is a neuroepidemiologist, and she helps lead the Harvard Football Players Health Study, which tracks thousands of former players. Basically, you know, these conditions like sleep apnea, low testosterone, high blood pressure, depression, these are all things that commonly afflict former football players, and they can all have symptoms that we might associate with CTE. But the key difference is that these conditions are treatable. CTE isn't yet. And so, and that's why researchers, and just like the NFL itself, the NFL Players Association, they're all aligned on this, just urging people to get treatment when you're having a health issue. And really, this study is a good reminder, I think, for more than just professional football players, just for everybody who plays football or any kind of contact sport, to take that advice.

• 15:23Speaker 01

  Right. I think you mentioned ice hockey and boxing earlier. So this isn't just like a football thing.

• 15:28Speaker 02

  No, it's, it's really the repeated impacts to the head that are the issue here. So honestly, soccer can be a big one, too. And when I was talking to Randall, he's the doctor at the University of Washington, he told me about his experience playing rugby and then spotting and consulting on concussions in the sport. And in that discussion, he, you know, made a point that stuck with me.

• 15:47Speaker 05

  I would not give up all of the pain in my shoulders and knees and, and all that for my time playing rugby. You know, it was an important part of my life, and, and I wouldn't want to give it up. But it has to be an informed choice, and we need to make it as safe as possible.

• 16:04Speaker 01

  Becky, thank you so much for bringing all this to us.

• 16:07Speaker 02

  Of course. Thanks for having me, Nate.

• 16:09Speaker 01

  Short waivers, if you were someone you know is considering suicide or is going through a mental health crisis, please call or text 988 to reach the suicide and crisis lifeline. Let's take care of each other. If you found this episode interesting, please follow us. We cover brain news pretty regularly. This episode was produced by Hannah Chin, edited by our showrunner Rebecca Ramirez and Russell Lewis. It was fact checked by Tyler Jones. The audio engineer was Jimmy Keeley. I'm Nate Rot. Thanks for listening to Short Wave, the science podcast from NPR.

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